Tripex mud pumps are commonly used in oilfield operations to pump fluid into a well. Instantaneous flow from a tripex mud pump can vary by approximately 23%, since the pump produces a maximum flow of about 106% during some crankshaft angles, and produces a minimum flow of 83% during other crankshaft angles. These varying flow rates tend to produce undesirable pressure changes or “noise” in the pumped mud which interferes with downhole telemetry and other techniques used during measurement while drilling or logging while drilling operations.
A quadruplex pump with four pistons or plungers also has a significantly high flow rate variation up to about 33%, while the flow rate for a sextuplex with six plungers is approximately 14%. Substantially reduced pressure variations can be achieved with a quintuplex pump, such as that disclosed in PCT/US2008/078720, wherein the pressure variation from a pump is approximately 7% or less.
In spite of the advantages of the quintuplex mud pump as disclosed in PCT/US2008/078720, the pump has disadvantages which have limited its acceptance. One such problem relates to the pinion gear, which at times must be replaced or refurbished. The long length of pinion gear makes it impractical in some installations with limited space to remove the pinion gear from the pump. Another significant problem with the quintuplex mud pump discussed above is that two bull gears driven by a common pinion shaft are used to power a common crankshaft, which commonly leads to one of the bull gears carrying a larger portion of the load than the other bull gear due to gear machining tolerances, thereby leading to excessive wear and maintenance problems. As a practical matter, these prior art bull gears use only one side of the gear tooth, and the other side of the gear tooth serves no practical purpose. There is no mechanism for effectively taking out backlash, and the two bull gears, if cut out of tolerance, must be recut.
The disadvantages of the prior art are overcome by the present invention, an improved quintuplex mud pump is hereinafter disclosed.